Remove support for `dyn*` from the compiler
This PR removes support for `dyn*` (https://github.com/rust-lang/rust/issues/102425), which are a currently un-RFC'd experiment that was opened a few years ago to explore a component that we thought was necessary for AFIDT (async fn in dyn trait).
It doesn't seem like we are going to need `dyn*` types -- even in an not-exposed-to-the-user way[^1] -- for us to implement AFIDT. Given that AFIDT was the original motivating purpose of `dyn*` types, I don't really see a compelling reason to have to maintain their implementation in the compiler.
[^1]: Compared to, e.g., generators whih are an unstable building block we use to implement stable syntax like `async {}`.
We've learned quite a lot from `dyn*`, but I think at this point its current behavior leads to more questions than answers. For example, `dyn*` support today remains somewhat fragile; it ICEs in many cases where the current "normal" `dyn Trait` types rely on their unsizedness for their vtable-based implementation to be sound I wouldn't be surprised if it's unsound in other ways, though I didn't play around with it too much. See the examples below.
```rust
#![feature(dyn_star)]
trait Foo {
fn hello(self);
}
impl Foo for usize {
fn hello(self) {
println!("hello, world");
}
}
fn main() {
let x: dyn* Foo = 1usize;
x.hello();
}
```
And:
```rust
#![feature(dyn_star)]
trait Trait {
type Out where Self: Sized;
}
fn main() {
let x: <dyn* Trait as Trait>::Out;
}
```
...and probably many more problems having to do with the intersection of dyn-compatibility and `Self: Sized` bounds that I was too lazy to look into like:
* GATs
* Methods with invalid signatures
* Associated consts
Generally, `dyn*` types also end up getting in the way of working with [normal `dyn` types](https://github.com/rust-lang/rust/issues/102425#issuecomment-1712604409) to an extent that IMO outweighs the benefit of experimentation.
I recognize that there are probably other, more creative usages of `dyn*` that are orthogonal to AFIDT. However, I think any work along those lines should first have to think through some of the more fundamental interactions between `dyn*` and dyn-compatibility before we think about reimplementing them in the type system.
---
I'm planning on removing the `DynKind` enum and the `PointerLike` built-in trait from the compiler after this PR lands.
Closesrust-lang/rust#102425.
cc `@eholk` `@rust-lang/lang` `@rust-lang/types`
Closesrust-lang/rust#116979.
Closesrust-lang/rust#119694.
Closesrust-lang/rust#134591.
Closesrust-lang/rust#104800.
Rollup of 12 pull requests
Successful merges:
- rust-lang/rust#136801 (Implement `Random` for tuple)
- rust-lang/rust#141867 (Describe Future invariants more precisely)
- rust-lang/rust#142760 (docs(fs): Touch up grammar on lock api)
- rust-lang/rust#143181 (Improve testing and error messages for malformed attributes)
- rust-lang/rust#143210 (`tests/ui`: A New Order [19/N] )
- rust-lang/rust#143212 (`tests/ui`: A New Order [20/N])
- rust-lang/rust#143230 ([COMPILETEST-UNTANGLE 2/N] Make some compiletest errors/warnings/help more visually obvious)
- rust-lang/rust#143240 (Port `#[rustc_object_lifetime_default]` to the new attribute parsing …)
- rust-lang/rust#143255 (Do not enable LLD by default in the dist profile)
- rust-lang/rust#143262 (mir: Mark `Statement` and `BasicBlockData` as `#[non_exhaustive]`)
- rust-lang/rust#143269 (bootstrap: make comment more clear)
- rust-lang/rust#143279 (Remove `ItemKind::descr` method)
Failed merges:
- rust-lang/rust#143237 (Port `#[no_implicit_prelude]` to the new attribute parsing infrastructure)
r? `@ghost`
`@rustbot` modify labels: rollup
`tests/ui`: A New Order [19/N]
> [!NOTE]
>
> Intermediate commits are intended to help review, but will be squashed prior to merge.
Some `tests/ui/` housekeeping, to trim down number of tests directly under `tests/ui/`. Part of rust-lang/rust#133895.
r? `@tgross35`
Start moving wf checking away from HIR
I'm trying to only access the HIR in the error path. My hope is that once we move significant portions of wfcheck off HIR that incremental will be able to cache wfcheck queries significantly better.
I think I am reaching a blocker because we normally need to provide good spans to `ObligationCause`, so that the trait solver can report good errors. In some cases I have been able to use bad spans and improve them depending on the `ObligationCauseCode` (by loading HIR in the case where we actually want to error). To scale that further we'll likely need to remove spans from the `ObligationCause` entirely (leaving it to some variants of `ObligationCauseCode` to have a span when they can't recompute the information later). Unsure this is the right approach, but we've already been using it. I will create an MCP about it, but that should not affect this PR, which is fairly limited in where it does those kind of tricks.
Especially b862d8828e is interesting here, because I think it improves spans in all cases
Replace `ItemCtxt::report_placeholder_type_error` match with a call to `TyCtxt::def_descr`
Fixesrust-lang/rust#143128.
We could likely use `tcx.def_descr` in more places (and therefore remove more `descr` methods). If it's something that we want to do, I can send a follow-up.
r? `@oli-obk`
`tests/ui`: A New Order [16/N]
> [!NOTE]
>
> Intermediate commits are intended to help review, but will be squashed prior to merge.
Some `tests/ui/` housekeeping, to trim down number of tests directly under `tests/ui/`. Part of rust-lang/rust#133895.
r? `@tgross35`
(just small one to test new method, also I should squash all this commits except move commit, so we after review will end up having like one move commit and one commit with changes, right?)
Do not freshen `ReError`
Because `ReError` has `ErrorGuaranteed` in it, it affects candidate selection and thus causes incompleteness which leads to weirdness in eval. See the comment in the test.
Also remove an unnecessary `lookup_op_method` since it doesn't effect tests.
Fixesrust-lang/rust#132882.
r? types
`tests/ui`: A New Order [13/N]
Some `tests/ui/` housekeeping, to trim down number of tests directly under `tests/ui/`. Part of rust-lang/rust#133895.
r? ```@jieyouxu```
`tests/ui`: A New Order [12/N]
Some `tests/ui/` housekeeping, to trim down number of tests directly under `tests/ui/`. Part of rust-lang/rust#133895.
r? `@jieyouxu`
New const traits syntax
This PR only affects the AST and doesn't actually change anything semantically.
All occurrences of `~const` outside of libcore have been replaced by `[const]`. Within libcore we have to wait for rustfmt to be bumped in the bootstrap compiler. This will happen "automatically" (when rustfmt is run) during the bootstrap bump, as rustfmt converts `~const` into `[const]`. After this we can remove the `~const` support from the parser
Caveat discovered during impl: there is no legacy bare trait object recovery for `[const] Trait` as that snippet in type position goes down the slice /array parsing code and will error
r? ``@fee1-dead``
cc ``@nikomatsakis`` ``@traviscross`` ``@compiler-errors``
add #![rustc_no_implicit_bounds]
Follow-up from rust-lang/rust#137944.
Adds a new `rustc_attrs` attribute that stops rustc from adding any default bounds. Useful for tests where default bounds just add noise and make debugging harder.
After reviewing all tests with `?Sized`, these tests seem like they could probably benefit from `#![rustc_no_implicit_bounds]`.
- Skipping most of `tests/ui/unsized` as these seem to want to test `?Sized`
- Skipping tests that used `Box<T>` because it's still bound by `T: MetaSized`
- Skipping parsing or other tests that cared about `?Sized` syntactically
- Skipping tests for `derive(CoercePointee)` because this appears to check that the pointee type is relaxed with `?Sized` explicitly
r? `@lcnr`
After reviewing all tests with `?Sized` and discussing with lcnr, these
tests seem like they could probably benefit from
`#![rustc_no_implicit_bounds]`.
Make missing lifetime suggestion verbose
I keep seeing this suggestion when working on rustc, and it's annoying that it's inline. Part of https://github.com/rust-lang/rust/issues/141973. Feel free to close this if there's another PR already doing this.
r? ``@estebank``
The version string is difficult to properly normalize out, and removing
it isn't a huge deal (the user can query version info easily through
`rustc --version` or `cargo --version`).
The normalization options were all non-ideal:
- Per-test version string normalization is nasty to maintain, and we
need to maintain `n` copies of it.
- Centralized compiletest normalization (with a directive opt-out) is
also not ideal, because `cfg(version(..))` tests can't have those
accidentally normalized out (and you'd have to remember to opt-out).
Several UI tests have a `normalize-stderr` for "you are using x.y.z"
rustc versions, and that regex is flexible enough for suffixes like
"-nightly" and "-dev", but not for "-beta.N". We can just add '.' to
that trailing pattern to include this.
`nominal_obligations` calls `predicates_of` on a `Sized` obligation,
effectively elaborating the trait and making the well-formedness checking
machinery do a bunch of extra work checking a `MetaSized` obligation is
well-formed, but given that both `Sized` and `MetaSized` are built-ins,
if `Sized` is otherwise well-formed, so `MetaSized` will be.
These tests just need blessing, they don't have any interesting behaviour
changes.
Some of these tests have new errors because `LegacyReceiver` cannot be
proven to be implemented now that it is also testing for `MetaSized` -
but this is just a consequence of the other errors in the test.
It seems like generics from `non_lifetime_binders` don't have any default
bounds like normal generics, so all of the `?Sized` relaxations need
to be further relaxed with `PointeeSized` for this test to be the
equivalent of before.
These tests necessarily need to change now that `?Sized` is not
sufficient to accept extern types and `PointeeSized` is now necessary. In
addition, the `size_of_val`/`align_of_val` test can now be changed to
expect an error.
With `MetaSized` bounds replacing `?Sized` and being added as a
supertrait, the same relaxations applied to the standard library must be
applied to minicore.
